Agricultural chemicals and fertilizers must be applied within very narrow time windows for maximum effectiveness. In some cases, this means that application must be performed after the crops have emerged, and sometimes even after the crops have grown to a height of several feet tall. To apply chemicals and fertilizers without damaging standing crops specialized self-propelled agricultural product applicators, having high ground clearance, such as so-called high-boy sprayers or dry product applicators, are often utilized with standing crops. The high ground clearance allows the applicator to move through the standing crops without damaging them. Such high ground clearance applicators also typically utilize independent drive and suspension systems for each wheel of the applicator, and provide some means for adjusting the track width of the wheels to match the row spacing of the crop being treated.
Achieving the high desired ground clearance presents unique problems in designing the main frame and suspension systems of the applicator. These problems are exacerbated by the operational necessities of having the applicator be capable of maneuvering across uneven ground, through ruts, ditches and waterways, carrying loads of thousands of pounds of dry or liquid agricultural product, while travelling at speed of up to 40 miles per hour. Having one of the wheels of the applicator drop into a ditch or impact a large rock while travelling fully loaded at high speed imposes major bending and twisting forces and stresses on the frame of the applicator.
It is also highly desirable to have the frame be as light as possible to reduce sprung weight of the applicator, so that the suspension components do not have to be sized to carry the additional weight, and to maximize payload of the applicator. To minimize sprung weight, the frames of prior applicators have utilized tubular frame members having a high section modulus and relatively low weight. Use of such tubular members has still resulted in frames that are heavier than desirable, in order to achieve the bending and torsional stiffness required for use in a self-propelled agricultural applicator.
The unique design constraints and operating environment of self-propelled agricultural product applicators precludes the use of many of the techniques used in producing frames and suspension systems for on-road vehicles, or off-road vehicles that do not require such extreme ground clearance.
It is desirable, therefore, to provide an improved frame having a calibrated bending and/or torsional stiffness gradient that is suitable for use in a self-propelled agricultural product applicator. It is also desirable to provide such an improved frame in a manner that is cost effective, and readily producible. It is further desirable to provide an improved frame that is as lightweight as possible, to minimize undesirable loading of suspension components and maximize payload of the applicator.